N-type Ge is obtained on doping the Ge-crystal with phosphorus.

Doping:

- Doping is the process of intentionally adding impurities to a semiconductor material to alter its electrical properties.
- In this process, a small amount of impurity atoms, called dopants, are added to the crystal lattice of the semiconductor.
- The dopants can either introduce extra electrons (N-type doping) or create electron deficiencies called holes (P-type doping) in the crystal structure.

N-type Doping:

- N-type doping involves adding impurities that introduce extra electrons into the crystal lattice of a semiconductor.
- This increases the concentration of free electrons, making the material conductive.
- In N-type Ge, phosphorus (P) is used as the dopant.

Why Phosphorus?

- Phosphorus is a group V element in the periodic table, meaning it has five valence electrons.
- When phosphorus atoms are introduced into the germanium crystal lattice, they replace some of the germanium atoms.
- Four of the valence electrons of the phosphorus atom bond with the neighboring germanium atoms, forming covalent bonds.
- The fifth electron, however, does not participate in bonding and becomes a free electron in the crystal lattice.
- These free electrons are responsible for the conductivity of the N-type Ge.

Role of Phosphorus:

- Phosphorus is a pentavalent dopant, meaning it has one more valence electron than germanium.
- This extra electron becomes a free electron in the crystal lattice, contributing to the conductivity of the material.
- The free electrons are easily excited by an electric field, allowing them to move and carry electric current.
- As a result, N-type Ge has a high electron conductivity.

Conclusion:

- N-type Ge is obtained by doping the Ge-crystal with phosphorus (P).
- Phosphorus, as a pentavalent dopant, introduces extra electrons into the crystal lattice, increasing its conductivity.
- These free electrons are responsible for the N-type behavior of the doped Ge material.